Magnetized record signal reproduction system



July 15,v 1958 A. M. SKELLETT 2,843,678

' MAGNETIZED RECORD SIGNAL REPRODUCTION SYSTEM Filed March 22, 1954 2 Sheets-Sheet 1 INVENTOR. ALBA-"er M. SKA-L 1.577

14770R/VEX' y 1958 A. M. SKELLETT 0 2,843,678

MAGNETIZED RECORD SIGNAL REPRODUCTION SYSTEM Filed. March 22, 1954 2 Sheets-Sheet 2 ALBERT I14- SKELLETT United States MAGNE'I'IZED RECORD SIGNAL REPRODUCTION SYS'lllilM Albert M. Skellett, Madison, N. .l., assignor to National Union Electric Corporation, Hatboro, Pan, a corpora tion of Delaware Application March 22,1954, Serial No. 417,667

8 Claims. c1. ire-100.2

This invention relates to magnetized recordsystems, and more especially it relates to systems for reproducing signals recorded on magnetized bands, wires, tapes and the like. I

A principal object of the invention is to provide an improved magnetized record and signal reproduction system of great sensitivity and freedom from the disturbing eifects of undesired magnetic fields of slowly varying intensity or of constant intensity.

Another object is to provide a signal reproducing system employing a defiectable cathode-ray beam controlled by a magnetized record, and including a novel beambalancing arrangement whereby the beam can be adjusted to its optimum position even though the cathoderay tube during use is subjected to undesirable magnetic fields of slowly varying intensity or of constant intensity.

A feature of the invention is to provide an improved and more sensitive signal reproduction system of the general kind disclosed in my cop'ending application Serial No. 227,594, fi ledMay'22, 1951, now Patent No. 2,720,-

558, issued Oct. ll, 1 955. v

A still further feature relates topthe novel combination and organization of elements and their relative interconnaction and location, and which'cooperate to provide an improved magnetic record controlled signal reproducing system. i l

Other features and advantages not-particularly enumerated will be apparent'after a consideration of the following detailed descriptions and the appended claims. In the drawing, v

, Fig. 1' is a composite schematic structural and wiring diagram of a reproduction and magnetic field indicating system according'to the invention;

Fig. 2 is a sectional view of the cathode-ray tube shown in Fig. 1, taken along the line 2- 2 thereof;'

Fig.3 is a modification of the system of Fig. 1.

- l have disclosed in my c'opending application Serial No; 227,594, filed May22, 19511, a system for translat- 'ing the magnetic record in a magnetized tape into electrical signals {through the "intermediary of a special design of cathode-ray tubel' While the system of 'my prior application has beenfound useful for the purposes therein designed, l have found that when ,itis operated in the .vicinity of disturbing magnetic fields either of slowly varying intensity or of constant intensity, the system is not always capable .of operating at maximum sensitivity. Fig. 1 .shows an arrangement for overcoming these disadvantages.

Referring, to Fig. .1, :there is-yshown in schematic form ianevaeuated enclosing ,hulb 10 of glass orother suitable material. Mounted within the bulb at one end thereof is any well -known'form of electron gun 1'1, compris- "in'g 'tore'xamplethe heatable electron-emitting cathode 12,"with -its internal 'heater filament l3; first accelerating and beam ifocusingvanoderltl; second or higher volt "age accelerating andbeam focusing anode 15. If des'ire'd, an aperturedicontrol zgrid.:(not shown.) may be 10- cated between the cathode 12 and the-anode 14 to control the intensity of the beam.

Suitably mounted'in the opposite end of the tube 10 are two metal plates or targets 16, 17. If desired, a

foraminous metal suppressor grid 18 may be located in front of the targets" in spaced relation thereto for the purpose of returning to the targets the secondary elec-. trons which may emerge'therefrom, i. e.,' suppressing them. If desired, the interior surface of tube 10fmay be provided with a coating of graphite; 20, which may be connected to the same potential as the anode 15. Suitably mounted within the tube 10, and located adjacent the exit end of gun 11', are twosoft-iron magnetic pole pieces 23, 24 (see Fig. 2), which define therebe tween a magnetic gap 25 which is in alignment with the 7 exit opening 26 of the electron gun. Mounted externally of the tube 10 are the soft-iron magnetic yoke members 27, 28, which are in magnetic alignment with the pole pieces 23, 24. The magnetic yokes extend ,away

from the bulb and their legs are in closely spaced relation to define the pick-up gap 29, past which the rec- T tentials are chosen so that the electrons in the beam 31 are focused to a relatively small spot 32.whose width is such that when the beam is undeflected, thespotsymmetrically overlaps the targets 16, 17, as shown inFig.

2. As a result of the varying flux across the gap 25 .con- V trolled by the m gnetization record in tape 30, the electron beam is shifted away from the target 16 and ,towards target 17, or vice versa, depending'uponthe rec- 0rd magnetization in the tape 30.

Surrounding the yoke 27 is a coil 33 consisting of two windings designated .34, 35, in Fig. 1. "'Likewisemounted on the yoke 28 is a coil 36, comprised of two windings 37, 33. The target 16 is connected through aresistance network consisting of the series-connected resistors 39, 40, 41, to the negative terminal 42 of adirect current biasing source 43, the positive terminal of which may be grounded. Likewise, the target 17 is connected through a resistance network consisting of the seriesconnected resistors 44, 45, 46, 'to the negative terminal 42.,

Each of the targets 16 and 17 is also connected through 7 a respective load resistor 47, 48 which can be connected through an output transformer 49 to asuitable signal utilization circuit. The resistors 47 and 48 are connected to the positive terminal 50 of the direct current power supply 51 which is also connected'through the windings 34, 37 to the plate or anode electrode 52 of a grid controlled amplifier tube 53; Similarly, the positive terminal 50 is connected through windings 3S and 33 to the plate or anode electrode '54 of a grid-controlled ar'nplifier tube 55 similar to tube 53. The control grid 56 is connected to the adjustable contact arm 57 which is adapted to be adjusted along the resistor 4!}. Likewise, the control grid 58 is connected to the adjustable contact arm 59 for adjustment along .theresistor 45. Thejcathode" 60 is returned to ground through thecathode load resistor 61. Likewise, the cathode 62 is returned to ground through its cathode load resistor 63; A condenser 64 is bridged directly across the grid 56 and ground .and a similar condenser 65' is bridged across grid 58 and ground. The condensers 64 and 65 serve as short oircuit paths to ground foralhbut athe VerylOwlfIeQIiency 2,843,678 1 Patented July 15, 1 958 p illariations of the potentials appearing at targets 16 and Resistors 39, 40 and 41 provide a direct current feed back path between the grid 56 and its cooperating plate or anode 52. Likewise, the resistors 44, 45 and 46 provide a direct current feed back path between the grid 58 and its associated anode 54. Preferably, the sum of resistors 39, 40 and 41, are of equal resistance to resistor 47 and the voltage from source 43 is such that approximately one-half of the voltage variation at target 16 is impressed directly on grid 56. Likewise resistors 44, #55 and 46 are of equal value to 48 and approximately onehalf of the voltage variation at target 17 is impressed directly upon grid 58.

As will be seen, the plate current flow between tl e anode and cathode of tube 53 flows through windings 34 and 37 in series. Likewise, the plate current flow between the anode and cathode of tube 55 flows in series through the windings 35 and 38. The windings 34, 35, 37 and 38 are preferably all of equal number of turns so that, when the beam 31 is in its neutral position where it symmetrically overlaps targets 16 and 17, then by appropriate adjustment of sliders 57 and 59 the current flow through windings 34, 35, will be equal and opposite. Likewise, the current flow through windings 37 and 38 will be equal and opposite and there will be no net magnetic field across the gap 25. If, however, the beam 31 is subjected to an external stray or undesirable magnetic field of slowly varying intensity or even of constant intensity the beam 31 will tend to wander from its normal symmetrical target overlap position. For example, it may move from target 17 towards target 16 to produce an unequal overlap. Therefore, the current through windings 34 and 35 will be unequal and will produce a resultant magnetic flux in the gap 25. The windings 37 and 38 are wound with respect to the wind ings 34 and 35 so that this unbalanced current through winding 34 will be in such a direction to magnetize the core 28 so that the beam is deflected back to its neutral position where it equally overlaps the two targets. At the same time the currents in windings 37, 38 will act in the same manner to give an added flux in the core 27 to assist the return of the beam to its neutral. or undeflected position. Thus, by this balanced arrangement, any stray magnetic field which tends to deflect the beam towards one of the targets causes the production of a rebalancing voltage which is impressed through the respective resistor networks 39, 40, 41 and 44, 45, 46 to cause the tubes 53, 55 to set up the required plate current flow through the windings 34, 37 and 35, 38 and thus to provide a counterbalancing magnetic field which restores the beam to its neutral or symmetric position.

In essence, therefore, the circuit comprises a feed back arrangement from the anodes of tube 53 and 55 by means of which the beam 31 is maintained at the optimum point of operation, namely where it divides itself substantially equally between the two targets 16, 17. Therefore, by choosing the proper values for condensers 64 and 65 and the associated resistor networks this feed back circuit is rendered effective only for slowly varying or constant stray magentic fields which tend to change the normal position of beam 31. On the other hand, for rapidly varying fields, such as those which are produced by the magnetized record in the tape 30 moving past a gap 29, the above described feed back or balancing circuit is effectively by-passed to ground, thus enabling the signal output circuit 49 to respond to the recorded signals without substantial degradation. By this arrangement it is possible to eliminate the detrimental effects of alternating current hum fields.

A volt meter 66 of the zero center reading type is connected through respective contacting sliders 67, 68 to the associated cathode load resistors 61, 63 so that the magnitude of the action of the feed back balancing circuit may be read in'volts. The purpose of the sliders 67, 68 is such that when the system is being initially set up 2,84c3,678- a e e for the balancing, the sliders 67, 68 can be adjusted to compensate for any variations in tubes 53, 55 or any variations in the associated circuit components. Normally the sliders 67, 68 are adjusted as close to the cathode end of their associated resistors 61, 63 as possible.

The system as shown in Fig. 1 may be used for other purposes than the reproduction of magnetic recorded signals in the tape 30. For example, the system can be used to measure stray magnetic fields occurring anywhere in space. The system is intially balanced at a non-stray field position, and when the tube 10 is brought into the presence of a stray magnetic field of slowly varying intensity or of constant intensity, the volt meter 66 gives a direct indication of the strength of that field and of its direction. If the system of Fig. l is to be used for hum bucking then the condensers 64 and 65 may be adjusted to such a value and may be connected in parallel with an appropriate inductance 69 or 70 so as to provide a parallel resonant circuit which can be tuned to the hum frequency, for example cycles per second. This enables the grids 56 and 58 to be short circuited to ground for this particular frequency. It will be understood, of course, that by proper choice of the condensers 64, and the tuning of this parallel resonant circuit the balancing out of the efiects of the stray magnetic fields at slower frequencies can also be accomplished.

Fig. 3 shows a modification of the system of Fig. 1 wherein the beam 31, instead of being automatically restored to its neutral or symmetric overlap position on targets 16 and 17 by means of magnetizing windings such as windings 34, 35 and 37, 38, is restored by means of electrostatic deflector plates 71, 72. In this embodiment, therefore, it is not necessary to provide the separate magnetizing windings on the cores 27 and 28. Therefore, the various elements of Fig. 3 which are identical with and operate the same as the corresponding elements of Fig. I bear the same designation numerals in both figures. In the embodiment of Fig. 3, the windings 34, 35, 37 and 38 are replaced by two load resistors 73, 74 and the resultant voltage drop across these resistors which is produced when the beam 31 tends to move from its neutral position when acted upon by stray fields is fed directly to the deflector plates 71, 72. This causes the beam 31 automatically to be restored to its neutral or symmetric overlap position on targets 16 and 17 while permitting the beam, of course, to be deflected in response to the higher frequency variations in the magnetic system 27, 28 produced by the moving tape 30.

Various changes and modifications can be made in the disclosed embodimentwithout departing from the spirit and scope of the invention.

What is claimed is:

1. Signal reproduction apparatus, comprising in combination, an electron discharge tube having means to develop a deflectable electron beam, means defining a magnetic circuit having a gap located within the tube and past which the beam moves, said magnetic circuit having another magnetic gap external of the tube and past which a signal-magnetized record is movable to control the magnetic flux in said circuit and thereby to vary the deflection of said beam in accordance with the signals in said record, a pair of output target electrodes in said tube upon which the beam is arranged normally to impinge in symmetric overlapped relation when said magnetic circuit is in its neutral flux condition, and circuit means also connected to said target electrodes and also controlling the beam deflection for automatically restoring said beam to its normal symmetrical target overlapped position when acted upon by a stray magnetic field of slowly varying intensity, the last-mentioned means comprising a pair of grid-controlled amplifier tubes, a frequency discriminating network connecting each target to the grid of a respective one of said pair of tubes, and a pair of differential magnetizing windings for said magnetic circuit said windings being connected in oppair of tubes.

posed balanced relation respectively to the anodes of said 2. Signal reproduction apparatus, comprising in comi bination, an electron discharge tube having means to develop a deflectable electronbeam, means defining a mag netic circuit having a gap located Within the tube and past which the beam moves, said magnetic circuit having another magnetic gap external of the tube and past which a signal-magnetized record is movable to control'the' mag- Qwhich the beam is arranged normally to impinge in symmetrically overlapped relation when said magnetic circuit "is in its neutral flux condition, and. circuit means also connected to said target electrodes and also controlling the beam deflection for automatically restoring said beam to its normal symmetrical target overlapped position when acted upon by astray magnetic field of slowly varying I intensity, the last-mentioned means including a pair of grid-controlled amplifier tubes each having a control grid connectedthrough a respective direct current resistance network to a corresponding one of said target electrodes,

i a pair of magnetizing windings for said magnetic circuit each connected respectively in the anode-cathode circuit of a respective one of said tubes, said windings producing a balanced difierential effect on said beam when it is in its normal symmetric target overlapping position and producing an unbalanced diflerential eiiect when the beam is afi'ected by a stray magnetic field and thereby maintaining the beam in its symmetric target overlapping .position when said magnetic circuit is in its neutral mag- ,netized condition.

3. Signal reproduction apparatusaccording' to claim 2, in which each of said resistance networks is by-passed to ground except for frequencies above apredetermined value corresponding to the rate of variation of said stray magnetic field. V v

4.. Signal reproduction apparatus according to claim a 2, in which the grid of each amplifier tube is by-passed to ground through a circuit which is tuned to resonance at a frequency corresponding to the rate of variation of said stray magnetic field.

5. Signal reproduction apparatus, comprising in combination, an electron discharge tube having means to develop a deflectable electron beam, means defining a magnetic circuit having a gap located within the tube and past which the beam moves, said magnetic circuit having another magnetic gap external of the tube and past which a signal-magnetized record is movable to control 7 the magnetic flux in said circuit and thereby to vary the deflection of said beam in accordance with the signals in said record, a pair'of output target electrodes in i said tube upon which the beam is arranged normally to impinge in balanced relation when said magnetic circuit is in a predetermined static condition, a first grid-controlled amplifier tube having its control grid connected to one of said targets, a frequency-discriminating by-pass circuit connected between the grid of said first tube and ground for shunting to ground variations of potential 'at said first target below a predetermined rate, a second grid-controlled amplifier tube having its control grid connected to the other of said targets, a frequency-discriminating by-pass circuit connected between the control grid of said second tube and ground for shunting to ground variations of potential at said second target below said predetermined rate, a plurality of coils. connected in balanced relation in the plate circuits of both of said tubes, said coils being coupled to said magnetic circuit to overcome the effect of stray magnetic fields'which tend' 6 to move said beam away from its balanced position on said targets.

6. Signal reproduction apparatus according to claim first and said third coils being wound in differential relation and coupled to. saidmagnetic circuit, said third and coupled to said magnetic circuit. 7 v

7. Signal reproduction apparatus, comprising incomfourth coils also being wound in differential relation and bination, an electron discharge tube having means' to develop a, deflectable electron beam, means defining a magnetic circuit having a gap located within thetube: and past which the beam moves, said magnetic circuit having another gap external of the tube and past which a signalmagnetized record is movable to control the magnetic flux in said circuit and thereby to vary the deflection of said beam in accordance with the signals in said record, a pair of output target electrodes in said tube upon which the beam is arranged normally to impinge in symmetric overlapped relation when said circuit is in its neutral flux condition, a pair of grid-controlled amplifier tubes having their control grids connected respectively to each one of said targets, means to energize the anodes of said amplifier tubes in balanced relation, a pair of electrostatic deflector elements for said beam, and means connecting said deflector elements respectively to the anodes of said pair of tubes to overcome the effect of stray magnetic fields which tend to move said beam away from'its symmetrical overlapped position with said targets. T

8. Apparatus of the type described, comprising incombination, an electron-discharge tube having means to develop a deflectab'le electron beam, a, pair of output target electrodes in said tube upon which the beam isiarr-anged normally to impinge in symmetrical overlapped relation,

' means defining a magnetic circuit having'a gap located within the tube and past which thebeam moves, means to excite said magnetic circuit to maintain said beam in a neutral'position where it symmetricallyoverlaps both said targets when said tube is not being subjected to an external unknown magnetic field, means to determine the magnitude of the unknown field to whichsaid beam is subjected, the last-mentioned means including a pair of grid-controlled tubes having their control grids connected respectively each to one of said targets, said tubes having a balanced output circuit which remains in balance as long as said beam is in symmetrical overlapped relation with said targets, indicator means connected to the cathodes of said tubes for producing an indication ofthe direction and strength of said unknown field, and separate circuit connections between said grid controlled tubes andi said. deflectable beamelect'ron discharge tube for automatically restoring the beam to a normal symmetrical target overlapping position when the beam is acted upon by a stray magnetic field of slowly varying intensity.

References Cited in the file of this patent :V

UNITED STATES PATENTS 2,165,307 Skellett July 1-1, 1939 2,599,949 Skellett June 10, 1952 2,613,340 Kliever Oct. 7, 1952 2,650,956 Heising Sept. 1, 1953 2,720,558 Skellett Oct. 11, 1955 2,725,430 Gnatian et al. Nov. 29, 1955 FOREIGN PATENTS 653,467 Germany Nov. 24, '1937 1 

